Surveillance applications, such as those incorporating full motion video, require transfer of large amounts of data. Efforts to reduce the performance requirements upon the data transmission system when large amounts of data must be transferred over the system have resulted in various data compression schemes. For example, video or graphical data may be compressed to occupy less space. Compressed data may then be transmitted and, because the data has been compressed into fewer information bits, fewer bits need to be transmitted, thereby relieving to some extent the loading upon the data transmission system. However, there are limits on the extent to which data may be compressed. In the past, compression imposed computational overhead upon the system and sometimes took too much time to complete. Compressed data must be decompressed at the destination at the other end of the transmission system in order to be useable, which imposes additional computational overhead upon the system. Although compression and decompression may be performed in software, the speeds at which such operations can be performed limit the usefulness of such techniques in some applications such as realtime full motion 30 frame per second video. If dedicated hardware is utilized, the additional hardware required to perform compression and decompression has limited the use in some applications where small size and miniaturization are required, and in other instances the cost of such additional hardware may be impractical.
Transmission of a real time video signal from a remote location to a base location is conventionally done by one of two methods: microwave or satellite. Equipment associated with these methods is extremely expensive and has significant limitations. The large amount of equipment necessary for satellite technology for remote transmission requires that the equipment be installed in trucks having an integral satellite dish. The signal is received from the video camera, beamed to the satellite, and then beamed to the base location for broadcast. Although the costs associated with satellite transmission are justifiable for large events such as sporting events where transmission could be made from a single location over a sustained period of time, the enormous amount of equipment and the sophisticated technology required makes satellite transmission extremely expensive and impractical for most surveillance applications.
Microwave transmission technology overcomes some of the limitations of satellite technology but has several additional limitations of its own. Microwave transmission systems are less expensive and require less equipment. With a conventional microwave system, a video signal is obtained and transmitted from the remote location at microwave frequencies from a vehicle mounted transmitting antenna to a base antenna for broadcast.
Difficulties have been encountered using this technology in aligning the antenna on the vehicle with the base antenna. Obstructions between the transmitting antenna and the base antenna may also prevent passage of the signal. Setup limitations also inhibit the use of microwave transmission systems in obtaining short segments of video at one location, transmission of that signal, moving to another location, transmission, movement, etc. Transmission is also limited to accessibility of the vehicle to the location of the subject matter.
Although advancements in cellular technology have allowed, cellular telephones to transmit voice messages and data such as facsimile and computer file transmissions from one location to another, this technology has never been used to transmit a high quality video signal.
The prior art in wireless LAN systems includes a variety of IR, or infrared, and RF, or radio frequency systems. Prior-art IR systems lack the bandwidth, optics or protocol to implement transmission of full motion 30 frame per second video. Prior art RF systems are either limited by spectrum availability to a data rate less than 10 Mbit/s, or designed for stationary mounting and ac-powered operation.
A need, therefore, exists in the art for a highly portable, cost-effective method and apparatus for capturing and transmission of real time quality video from a remote location to a base location. A need also exists for a capability for further retransmission of the video signal from the remote location through the base location apparatus over computer network, land lines, or other network to multiple users in diverse geographic locations.